The present invention relates to an AC generator (i.e., also-called alternator) for an automotive vehicle, which is preferably installed in a passenger vehicle or a truck or the like.
To reduce the aerodynamic resistance while traveling, vehicle body tends to be formed into a slant nose shape. Securing a sufficient space for a passenger compartment is of great concern. To satisfy these requirements, engine rooms of automotive vehicles have been becoming so narrow and crowded such that now only a limited amount of space is available for instaling an AC generator. Meanwhile, to improve fuel economy, rotation of an engine tends to be decreasing. Correspondingly, rotation of the AC generator is lowered. On the other hand, there is a need to increase the electric load for safety control devices etc. Thus, improving the generating performance of the AC generator is strongly required. In other words, a compact, powerful, and non-expensive automotive AC generator is required.
To this end, the power output may be increased by reducing the winding resistance and air gaps or by increasing an exciting current. However, this will induce heat generation at various components constituting the AC generator. Especially, rectifying elements (i.e., diode) are subjected to a large temperature increase. The rectifying elements are generally used to rectify electric power when generated by a stator from AC voltage into DC voltage. To secure the reliability of this rectifying element, it is necessary to cool the cooling fin satisfactorily within a limited space. To improve the cooling performance, it is of course possible to enlarge the cooling fan so as to increase an amount of cooling air. However, solely increasing the cooling air volume will result in an increase of noise.
FIG. 4 shows an automotive AC power unit for a conventional automotive AC generator.
Cooling fins 511 and 512, used for cooling the rectifying elements, are disposed on a rear frame. An IC regulator 7 and a connector casing 8 are disposed at point-symmetrical positions with respect to the cooling fins 511 and 512, respectively. A brush holder 6 is disposed at a portion surrounded by them. An appropriate clearance is provided at a radial-inner end and a radial-outer end of each of the cooling fins 511 and 512. More specifically, as shown in FIG. 5, the radial-inner end of each cooling fin 511 or 512 is spaced from a slip ring protector 91 with a radial clearance while the radial-outer end is spaced from a rear cover 92 with another radial clearance. The cooling fins 511 and 512 have circumferential ends which are partly brought into contact with neighboring components so as to provide open spaces 93.
A central portion of each of the cooling fins 511 and 512 is sufficiently cooled by cooling air, as the cooling air is introduced from an opening provided on the rear cover 92 and flows along the surfaces of these cooling fins 511 and 512, as shown in FIG. 5. However, the cooling air does not flow at the above-described contacted end portions of the cooling fins 511 and 512. Meanwhile, the cooling air flow resistance is lowered significantly at the opened end portions of the cooling fins 511 and 512, compared with other portions where components are disposed. Thus, the introduced cooling air may directly go out through the opened end portion without interacting with the cooling fins 511 and 512. Accordingly, cooling performance is not uniform among a plurality of diodes 513 and 514 arranged in a circumferential direction on the cooling fins 511 and 512. More specifically, the diodes 513 and 514 positioned at the circumferential ends of the cooling fins 511 and 512 are not satisfactorily cooled by the cooling air, compared with the diodes 513 and 514 positioned at the circumferential centers of the cooling fins 511 and 512.
U.S. Pat. No. 4,952,829 discloses a cooling fin for a rectifying element which has a sectorial opening at a radial-outer end of a brush holder. This arrangement will encounter with the above-described problem that the rectifying elements positioned near the opening are not sufficiently cooled because the cooling air is directly guided to the opening.
In view of the foregoing problems encountered in the prior art, the present invention provides an automotive AC generator which is capable of improving the cooling performance of rectifying elements in a crowded space accommodating a brush holder, an IC regulator and a connector casing by increasing an effective cooling area of a cooling fin while adequately maintaining the cooling performance of other components.
In order to accomplish the above-described and other related objects, the present invention provides a novel and excellent automotive AC generator characterized by the following features. A cooling fin (511, 512), fixed to a frame (42), mounts a plurality of rectifying elements (513, 514) rectifying a generated power. A brush holder (6) includes a brush container (62) accommodating a brush (61) and a brush container fixing arm (63) supporting the brush container (62). A connector casing (8) has terminals (81) for inputting and outputting electric signals from and to a vehicle electric apparatus. An IC regulator (7) adjusts an output value of the generated voltage. A circumferential width of the IC regulator is substantially identical to a circumferential width of the brush container (62). The cooling fin is configured into a circular ring shape separated at a cutout section (52). The brush holder, the connector casing and the IC regulator are disposed in the cutout section. And, a circumferential gap (B) of the cutout section is smaller than three times a circumferential width (A) of the brush container.
According to the above-described arrangement, the brush holder, the connector casing and the IC regulator are disposed in the cutout section of the cooling fin. This arrangement is advantageous in that the cooling fin for the rectifying element can be extensively provided along an entire circumferential region except for the brush holder. Not only the effective surface area of the cooling fin is increased, but also the cooling air can flow uniformly and effectively along the entire circumferential region. Thus, the cooling performance can be greatly improved.
The circumferential gap of the cutout section of the cooling fin has a sensitive correlation with generation of useless cooling air. In other words, the circumferential gap of the cutout section gives a large influence to the cooling performance of the rectifying elements located on the cooling fin, especially in the vicinity of the cutout section.
Hence, the inventors of the present invention have conducted a test to check the temperature increase in a rectifying element located in the vicinity of the cutout section of the cooling fin when a ratio B/A is varied. According to a test result shown in FIG. 3, the temperature of the rectifying element can be effectively suppressed when the ratio B/A is smaller than 3.
In addition, both the brush holder and the connector casing can be securely fixed to the cooling fin by using shorter fixing arms. This is advantageous in that fixing strength and vibration durability can be improved for the brush holder and the connector casing.
Preferably, the circumferential gap (B) of the cutout section is in a range of 1.5 to 2.8 times the circumferential width (A) of the brush container.
Preferably, the IC regulator (7) is connected to at least one of the brush holder (6) and the connector casing (8) with a clearance so that cooling air can flow along a surface of the IC regulator. With this arrangement, it becomes possible to effectively cool the IC regulator which is a beat generating member as well as the rectifying elements.
Preferably, the cooling fin comprises a positive-electrode fin (511) and a negative-electrode fin (512) arranged in parallel to each other via an insulating member (516). In this case, the positive-electrode fin. is a cooling fin attached to higher-voltage side rectifying elements which serve as an upper arm of an ordinary three-phase full-wave rectifying circuit. The negative-electrode fin is a cooling fin attached to a lower-voltage side rectifying element which serves as a lower arm of this three-phase full-wave rectifying circuit. This arrangement is advantageous for the cooling air. The cooling air flows in an axial direction from a rear side of an automotive AC generator in response to a revolution of the rotor (3). The cooling air can be smoothly conveyed to the cooling fins (511, 512). This makes it possible to cool the cooling fins effectively. Furthermore, the effective area of the cooling fins can be increased. Thus, the cooling performance can be greatly improved.
Preferably, a capacitor (85) is connected between power supplying terminals (82, 82) of a rectifying circuit including the rectifying elements, and the capacitor is disposed in the cutout section (52). This arrangement is advantageous in that wiring layout can be simplified. This makes it possible to remove ripple components from a DC output voltage generated from the rectifying circuit. Furthermore, no extra space is required for the electric noise-reducing capacitor. Thus, the effective area of the cooling fin can be adequately maintained.
Preferably, the IC regulator (7). has a one-chip integrated circuit arrangement including an integrally molded cooling fin (73). This arrangement is advantageous because no regulator casing is required and, as a result, the space for the regulator can be reduced significantly. Accordingly, the effective area of the cooling fin can be increased. The cooling performance can be improved.
Reference numerals in parenthesis, added in the above description, show the correspondence to the components disclosed in a later-described preferred embodiment of the present invention. Therefore, these numerals are merely used for expediting the understanding to the present invention and not used for narrowly interpreting the scope of the present invention.